Form validation is broken
HTML Forms' validation is based on the form's post meta. When a form is saved in the WP backend, the required & e-mail fields are serialized & saved to _hf_settings. The required fields are extracted with JS from the #hf-form-editor field, which is populated by the post content.
A possible solution would be to ask the HTML forms plugin creator to add a filter to functions.php:100 return $form;, so we can inject our form code (everything inside the
I don't have a solution for this inside of the package but take a look at https://gist.github.com/Log1x/35f3f1f20e430d6a36a0c2e8e8f13ffc if you want to manually add form validation. It also includes an example for implementing Google reCAPTCHA.